This research concentrates on several related subjects. 1. Analysis of the mechanics and significance of the covalent interaction of aminoacyl tRNA synthetases with uridine and the relationship of this phenomenon to the recognition of transfer RNAs; 2. Affinity labeling of aminoacyl tRNA synthetases and characterization of active site peptides; 3. Regulation of the expression of genes for aminoacyl tRNA synthetases as studied by in vitro transcription and related investigations; 4. Recognition of specific DNA sequences by aminoacyl tRNA synthetases, in connection with their autogenous regulation of transcription; 5. Cloning and sequencing genes for aminoacyl tRNA synthetases; 6. Related studies of gene regulation in eukaryotes.